On the fault tectonics of the Baruun Huuray basin by using Remote Sensing images

On the fault tectonics of the Baruun Huuray basin by using Remote Sensing images

G. Badarch, D. Dorjnamjaa
Geological Institute of Mongoliah Academy of Sciences
Ulaanbaatar 210351, Mongolia

M. Saandar
Remotes sensing and Geoinformation Center
MGGE, Mongolia

Abstract
This paper discusses the geodynamic environment of formation of the heterogeneous faults within the Baruun Huuray basin. On the remoe sensing images, in the northern side of the basin is established the Bulgan and Mergen thrusts, Turgen and Huvch strike slip faults. Southward of the basin occurred a series of left-lateral strike slip on the northeast trending and a lineer-fold of noth-west trend. The heterogenous faults of the Barun Huuray basin formed during the Late Paleozoic and Cenozoic period.

1. Introduction
The Baruun Huuray basin lies on the western part of the variscides of Southern Mongolia and adjacent to the area of Northwestern China. Previous work in Mongolia ( Tikhonov, 1974; Khilko et al. 1985 ) and China (Wenjun, 1968; Peizhen, 1982; Tapponnier et al. 1979 ) described several strike slip faults and thrusts. However, new data on the fault tectonics of the Baruun Huuray basin by using remote sensing images and as a results of our fieldwork is obtained in the last year.

2. Geology of the Baruun Huuray basin
The study area can be divided into two main tectonic zones such as Northern Baruun Huuray and Southern Baruun Huuray ( Badarch, 1990). Besides, along the Bulgan fault extended narrow tectonic wedge (Bizh), which is characterized by Lower – middle Devonian tholeiitic basaltsm tuffs, cherts, sandstones and siltstones (Fig. 2 ) . This Bizh wedge is analogy to the Ertysh zone of Northern Junggar ( Wenjin, 1968).

The Northern Baruun Huuray zone consists of Devonian and Lower Carbonierous alkaline volcanic rocks, includes trachyandesites,

Quartz lattes, trachydacites, rhyodacites and shoshonites. This volcanic series formed in the continental crust of the active margin.

The Southern Baruun Huuray zone is characterized by Devonian tholeiitic pillow lavas, calc-alkaline basalts, basaltic andesites, dacites, tuffs, siliciliths and volcaniclastic turbidities; the volcanic rocks are covered of Lower Carboniferous flysch like deposites. The west ( in China ) this zone consists of the Armantai ophiolite zone ( Wenjum, 1968 ). In opaleotectonic aspect the Southern Baruun Huuray zone treats of frontal arc, fore-arc and back-are basins.

3. Fault tectonics of the Baruun Huuray basin
Thrust and strike slip faulting play key roles in the tectonics of Baruun Hurray basin. The Bulgan thrust is clear on the space imagery of the Southwestern end of Mongolian Altay and southward over thrusting of Lower Paleozoic metamorphic rocks onto Devonian volcanic series of the Bizh wedge (Fig. 2). This fault is Eastern continuation of the famous Irtysh zone compression (Fig. 1). Qu Guosheng ( 1990 ) reported some features of the Irtysh zone as composite thrust systems in Chinese Altay.

Fig. 1 Map of major faults, intramontane basins and location of Fig. 2 in southeastern Kazakstan, northwestern China and western Mongolia

Fig. 2 Simplified geologic man of the Baruun Huuray basin ( riginally mapped from space image (AT) at a scale of 1:1,000,000; Adapted from 1:2,000,000 EGXP map ( 1985). Faults: F1-Sulgan, L-1 eren, b-baruun Huuray, C- Taniyn Shar; Uphiolites: a armantai, K-Karamleile
On the southern flank of the basin or in the Southern Baruun Huuray zone several left-lateral faults trend northeast and east. Between those faults occurred the isoclinal and tight folded Devonian and carboniferous rocks (Fig. 2). The left – lateral movement of the strike slip faults and the Bulgan and Mergen therusts caused the northward movement of Southern Baruun Huuray volcanic arc, when the Middle Paleozoic Karameile ocean was closed ( Carrol et. al. 1990 ). Because the active tectonics is affected by the earlier geologic history of the area.

The major right – lateral strike slip on the northwest trending ( Fu Yun, Turgen and Huvch ) and some left-lateral strike slip on the west-southewest trending ( Bulgan and Tahiyn Shar ) associated with these earthquakes. These very young faults formed the rapid deformation in Western Mongolia after collation of India with Asia.

4. Conclusion
The Barun Hurray basin suffered two stages of faulting and active deformation. The major thrust and left – lateral strike.

Slip faults formed in the late Paleozoic time. Right –lateral strike slip faults extending to the northwest and the left-lateral strike slip faults on the west-southwest trending are happened during the Genozoic time.

References

Badarch G. Tectonics of fold belts of Southern Mongolia. Ulaanbaatar, 1990 ( in Russia)
BGXP ( bureau of Geological and Mineral Resources of Xingiang Province ). Geological map of Xinjiang Uygur Autonomous Region. Beijing, Geological Publishing House, scale 1:2,000,000. 1985 Carroll A.R., Liang Y., Graham A.S., Xiao X., Hendrix S.M., Chu J., McKnight C.L. Junggar basin, northwest China: trapped Late Paleozoic ocean. Tectonopysics, 181: 1-14, 1990.
Khilko S.D., Kurushin R.A., Kochetkov V.M. Misharina L.A., Melnikova V.I., Gilyova N.A., Lastochkin S.V., Balzhinnyam I., Monhoo D. Earthquakes and the bases of the seismic zoning of Mongolia. Nauka, Moscow, 1985. ( in Russian ).
Peishen ZZhang. Surface ruptures associated with the 1931 Fu Yun, northwestern China, earthquake, Masters thesis, Chinese University of Science and Technology, 1982. ( in Chinese )
Guocheng Qu. Thrust systems in Chinese Altaides. Report 1, of the IGGF, project 283: Geodynamic evolution of Paleoasian ocean, Novosibirsk, 1990.
Tapponnier P., Molnar P. Active faulting and Cenozoic tectonics of the Tien Shan, Mongolian and Baykal Regions. J. Geophys. Res. 84, 3425 3459, 1979.
Tikhonov V.I. Faults. Tectonics of the Mongilian People s Republic, pp. 196 – 209, Nauka, Moscow, 1974. ( in Russian )
Wenjun C. Preliminary study on Flate Tectonics on Northern East Junggar in Xinjiang Uygur Autonomous Region. Contrib. Proj. Plate Tectonics, North China, no 1, pp. 1-21. Geol Pub. House, Beijing, 1983. ( in Chinese )